Femoral Prosthesis with Insertion/Extraction Feature

ABSTRACT

A femoral prosthesis system is provided which includes femoral prosthesis and an instrument for inserting/extracting the femoral prosthesis. The femoral prosthesis includes a stem and a neck portion. The stem includes a proximal end portion which defines a proximal stem axis. The neck portion is located proximally of the proximal end portion. The neck portion includes a proximal surface and an insertion/extraction cavity which extends distally from the proximal surface. The insertion/extraction cavity is configured to couple with the insertion/extraction instrument. The insertion/extraction cavity defines an insertion/extraction cavity axis which, when projected onto a coronal plane including the proximal stem axis, is not parallel with the proximal stem axis. The insertion/extraction instrument includes a distal end portion configured to couple with the insertion/extraction cavity.

FIELD

This disclosure relates generally to femoral prostheses and, morespecifically, to features facilitating insertion and extraction offemoral prostheses.

BACKGROUND

Hip arthroplasty can be used to restore function to an injured ordiseased hip joint. When performing surgical procedures such as hiparthroplasty, physicians generally attempt to damage as little tissue aspossible to minimize trauma to the patient, reducing the time and effortrequired for the patient's recovery. To facilitate this goal, advancesin medical technology have enabled minimally invasive surgicalprocedures, wherein a minimally necessary number of incisions are madeand the incisions are as small as functionally possible. Accordingly, inminimally invasive procedures, the openings through which physiciansperform procedures are relatively small, resulting in a limited range ofmotion and maneuverability for procedural tools and equipment. Thus,minimally invasive procedures provide benefits, such as minimizingtrauma to the patient and reducing the patient's recovery, as well aschallenges, such as reducing the workspace and range of motion forphysicians and their tools during procedures.

For the purposes of surgical procedures, such as hip arthroplasty,positions and directions relative to the hip joint may be describedusing anatomical directions. Accordingly, as used herein, proximalrefers to the direction toward to the hip joint, distal refers to thedirection away from the hip joint, anterior refers to the directiontoward to the front of the body, posterior refers to the directiontoward to the back of the body, medial refers to the direction toward tothe centerline of the body and lateral refers to the direction away fromthe centerline of the body. Additionally, aspects of the hip joint canbe described relative to the anatomical planes: the transverse plane,which divides the body into a superior portion (nearer to the head) andan inferior portion (nearer to the feet); the sagittal plane, whichdivides the body into a left portion and a right portion; and thecoronal plane, which divides the body into the anterior portion and theposterior portion.

In a total hip arthroplasty, both the “ball” and the “socket” of the hipjoint are replaced with prosthetic device implants to form a new joint.The ball of the hip joint is often replaced by removing the femoral headfrom the proximal end of the femur, inserting a femoral prosthesispartially into the intramedullary canal of the femur, and coupling aball to the proximal end of the femoral prosthesis. The socket of thehip joint is often replaced by removing bone from the acetabulum tocreate a cup-shaped opening and inserting an acetabular cup prosthesisinto the cup-shaped opening. In a partial hip arthroplasty, either theball or the socket of the hip joint may be replaced with a prostheticdevice. If, after a total or partial hip arthroplasty, a subsequentmedical event arises involving one of the hip implant prostheses, aprocedure may be required to extract or remove the implanted prostheticdevice to enable replacement with another prosthesis.

Inserting and extracting a femoral prosthetic device from a patient'sfemur generally require specific tools which engage with the femoralprosthetic device and enable a physician to apply sufficient force tothe femoral prosthetic device. Because a tight fit between the femoralprosthetic device and existing femoral bone is desired, both insertionand extraction of a femoral prosthetic device generally requiresapplication of a significant impact force to the femoral prostheticdevice. Such an impact force is usually applied to an impact surface onthe tool. The impact force is transferred through the tool to thefemoral prosthetic device.

Due to the anatomy of the hip joint and the reduced range ofmaneuverability in minimally invasive hip arthroplasties, the tools forinsertion and extraction are generally curved, like that in FIG. 1, toaccommodate available access angles and to avoid unwanted contact withand impingement of bones and tissues during the procedures. The curvedshapes of the tools, while providing some benefits, in turn presentadditional challenges and difficulties during insertion and removal offemoral prosthetic devices.

As shown in FIG. 1, for example, because the tool 10 is curved, theimpact force F₁ applied to the impact surface 12 by the physician isoffset from the transfer location 14 where the force is applied to thefemoral prosthetic device through the tool 10. One problem that arisesas a result of this offset 16 is the generation of a moment M about thetransfer location 14. In other words, application of the impact forceF₁at the impact surface 12 generates a tendency for the tool 10 torotate about the transfer location 14. Accordingly, to prevent the tool10 from rotating about the transfer location 14 and maintain stabilityof the tool 10 during the procedure, the physician must apply a manualforce F_(M) to the tool 10 to oppose the moment M generated by theimpact force F₁.

By way of example, if the offset 16 between the axis of the impact forceF₁ and the transfer location 14 is 50 mm and the physician grips thetool 10 at a gripping offset 22 that is 230.7 mm from the transferlocation 14, the moment M generated at the transfer location 14 has amagnitude that is approximately ⅕ the magnitude of the impact force F₁.Accordingly, to oppose the moment M, the physician must apply a manualforce F_(M) that is approximately ⅕ the magnitude of the impact forceF₁. If the impact force F₁ is, for example, 500 lbf, a physician has toapply a manual force F_(M) that is approximately 100 lbf while alsomaintaining proper positioning of the instruments.

Another problem that arises due to the generated moment M is that thetip 18 of the tool 10 which engages the femoral prosthetic device at thetransfer location 14 can be sheared off, becoming lodged in the femoralprosthetic device. As noted above, to counteract the moment M generatedby the impact force F₁ applied to the tool 10, physicians must apply asufficient opposing manual force F_(M). Instead of applying the manualforce F_(M) to oppose the moment M, however, some physicians haveintuitively attempted to eliminate the moment M by hitting the edge ofthe impact surface 12, thereby applying the impact force F₁ at an angle20 relative to the impact surface 12. By applying the impact force F₁ tothe tool 10 at an angle 20, however, the physician generates asignificant shear stress F_(S) on the tip 18 of the tool 10 whichengages the femoral prosthetic device. The shear stress F_(S) hasresulted in shearing off the tip 18 of the tool 10, requiring additionalcorrective measures to be undertaken during the procedure.

Given the above discussion, it would be advantageous to provide animproved femoral prosthesis including features enablinginsertion/extraction with greater efficiency and less risk for error. Itwould also be advantageous to provide an improved insertion/extractiontool including features enabling insertion/extraction with greaterefficiency and less risk for error. It would also be advantageous toprovide an improved method for inserting/extracting femoral prostheticdevices with greater efficiency and less risk for error.

SUMMARY

In accordance with one embodiment of the disclosure, there is provided afemoral prosthesis including a stem and a neck portion. The stemincludes a proximal end portion which defines a proximal stem axis. Theneck portion is located proximally of the proximal end portion. The neckportion includes a proximal surface and an insertion/extraction cavityextends distally from the proximal surface. The insertion/extractioncavity is configured to couple with an insertion/extraction instrument.The insertion/extraction cavity defines an insertion/extractioninstrument coupling axis which, when projected onto a coronal planeincluding the proximal stem axis, is not parallel with the proximal stemaxis.

In accordance with another embodiment of the disclosure, there isprovided a femoral prosthesis system including a femoral prosthesis andan insertion/extraction instrument. The femoral prosthesis includes afemoral stem and a neck portion. The femoral stem has a proximal endportion which defines a proximal stem axis. The neck portion is locatedproximally of the proximal end portion. The neck portion includes aproximal surface and an insertion/extraction cavity extends distallyfrom a proximal surface. The insertion/extraction cavity defines aninsertion/extraction instrument coupling axis which, when projected ontoa coronal plane including the proximal stem axis, is not parallel withthe proximal stem axis. The insertion/extraction instrument includes adistal end portion configured to couple with the insertion/extractioncavity.

In accordance with yet another embodiment of the disclosure, there isprovided a method of inserting a femoral prosthesis including couplingan insertion/extraction instrument to the femoral prosthesis, insertinga distal end portion of the femoral prosthesis into a femur, andimpacting a proximal end portion of the insertion/extraction instrument.The instrument includes a body defining a longitudinal axis and thefemoral prosthesis includes a proximal portion and a stem portiondefining a longitudinal axis. Coupling the insertion/extractioninstrument to the femoral prosthesis includes coupling the instrumentwith the proximal portion of the femoral prosthesis such that thelongitudinal axis of the body of the instrument is not parallel with thelongitudinal axis of the stem portion of the femoral prosthesis.

The above described features and advantages, as well as others, willbecome more readily apparent to those of ordinary skill in the art byreference to the following detailed description and accompanyingdrawings. While it would be desirable to provide a femoral prosthesisand femoral prosthesis system that provides one or more of these orother advantageous features, the teachings disclosed herein extend tothose embodiments which fall within the scope of the appended claims,regardless of whether they accomplish one or more of the above-mentionedadvantages.

BRIEF DESCRIPTION OF THE DRAWINGS

Features of the femoral prosthesis and the femoral prosthesis system areapparent to those skilled in the art from the following detaileddescription with reference to the following drawings.

FIG. 1 depicts a side plan view of a prior art tool used to transfer anapplied force to a femoral prosthesis during a hip arthroplastyprocedure.

FIG. 2 depicts a side plan view of a femoral prosthesis to be used inhip replacement.

FIG. 3 depicts a fragmentary side plan view of the femoral prosthesis ofFIG. 2, wherein a proximal portion of the femoral prosthesis is shownfor clarity.

FIG. 4 depicts a fragmentary top perspective view of the femoralprosthesis of FIG. 2, wherein a proximal portion of the femoralprosthesis is shown for clarity.

FIG. 5 depicts a side plan view of an insertion/extraction instrument tobe used to insert or extract the femoral prosthesis of FIG. 2.

FIG. 6 depicts a cross-sectional view of the side of the femoralprosthesis of FIG. 2, wherein a proximal portion of the femoralprosthesis is shown for clarity, with a fragmentary side plan view ofthe insertion/extraction instrument of FIG. 5, wherein a distal portionof the insertion/extraction instrument is shown for clarity.

DETAILED DESCRIPTION

As shown in FIG. 2, the femoral prosthesis 100 includes a stem 104, aneck portion 108, and a femoral head fitting 112. The neck portion 108extends proximally from the stem 104 and the femoral head fitting 112extends proximally from the neck portion 108. The stem 104, neck portion108, and femoral head fitting 112, in one embodiment, are formed fromone piece of material and, in another embodiment, are formed fromindividual pieces of material that are subsequently coupled together.

The stem 104 includes a stem proximal end portion 116, a stem distal endportion 120 and a stem body portion 124. The stem 104 is constructed outof a metal or alloy, such as for example, a titanium alloy, or anothermaterial known in the art to have similar properties desirable for longterm implantation into the femur. The stem 104 is substantially straightalong the stem body portion 124 from the stem proximal end portion 116to the stem body portion 124. The stem proximal end portion 116 definesa longitudinal axis, referred to herein as a proximal stem axis 128,extending axially through the approximate center of the stem proximalend portion 116. When the stem proximal end portion 116 is projectedonto a transverse plane, the proximal stem axis 128 extends in adirection substantially perpendicular to the transverse plane.

The stem body portion 124 extends between the stem proximal end portion116 and the stem distal end portion 120 and has a generally elongatedshape. The stem body portion 124 in one embodiment includes a taper suchthat the stem body portion 124 is smaller nearer to the stem distal endportion 120 and larger nearer to the stem proximal end portion 116. Thetaper is sized and configured to facilitate insertion of the femoralprosthesis 100 into an intermedullary canal of a femur.

The neck portion 108 extends proximally from the stem proximal endportion 116 and includes a neck proximal end portion 152, a neck distalend portion 156, a neck medial portion 160 and a neck lateral portion164. The neck medial portion 160 and the neck lateral portion 164 extendbetween the neck proximal end portion 152 and the neck distal endportion 156 and are arranged opposite one another along the neck portion108. The neck lateral portion 164 includes a shoulder 176. Inparticular, the neck portion 108 is shaped such that the neck lateralportion 164 is more medial at the neck proximal end portion 152 than atthe neck distal end portion 156 forming the shoulder 176.

The neck distal end portion 156 is located adjacent to the stem proximalend portion 116 and the neck proximal end portion 152 extends proximallyfrom the neck distal end portion 156. The neck proximal end portion 152includes a proximal surface 180 extending along at least a portion ofthe neck proximal end portion 152 and the neck lateral portion 164. Theproximal surface 180 is oriented such that it substantially facesproximally away from the stem 104 and the neck portion 108.Additionally, when the neck proximal end portion 152 is viewed in atransverse plane, the proximal surface 180 is substantially parallel tothe transverse plane.

The neck proximal end portion 152 also includes an insertion/extractioncavity 184 extending distally into the proximal surface 180 as shown inFIG. 3. The insertion/extraction cavity 184 includes aninsertion/extraction cavity axis 200. The insertion/extraction cavity184 extends distally into the proximal surface 180 at an angle A that isnot orthogonal to the proximal surface 180. In particular, as describedin more detail below, as the insertion/extraction cavity 184 extendsdistally, it also extends laterally.

With reference to FIG. 3 and FIG. 4, the neck proximal end portion 152and the insertion/extraction cavity 184 are described in more detail. Asshown, the insertion/extraction cavity 184 includes an instrumentreceiving portion 188, a prosthesis keyed portion 192, and a prosthesisthreaded portion 196. The instrument receiving portion 188 is locateddirectly distally to the proximal surface 180 and is open to theproximal surface 180. The instrument receiving portion 188 has aninstrument receiving portion depth 204 (shown in FIG. 3) definedrelative to the proximal surface 180. The instrument receiving portion188, in this embodiment, is also in open communication with both theprosthesis keyed portion 192 and the prosthesis threaded portion 196. Insome embodiments, however, the instrument receiving portion 188 is notin open communication with the prosthesis keyed portion 192.

The prosthesis keyed portion 192 is also located directly distally tothe proximal surface 180 and is open to the proximal surface 180. Theprosthesis keyed portion 192 has a prosthesis keyed portion depth 208(shown in FIG. 3) defined relative to the proximal surface 180, and theprosthesis keyed portion depth 208 is shallower than the instrumentreceiving portion depth 204. The prosthesis keyed portion 192 is offsetlaterally from the instrument receiving portion 188.

The prosthesis threaded portion 196 extends distally from the instrumentreceiving portion 188. The prosthesis threaded portion 196 (shown inFIG. 3) is defined by a wall 216. The prosthesis threaded portion 196includes threads (not shown) extending into the wall 216.

The insertion/extraction cavity axis 200 extends axially through thecenter of the instrument receiving portion 188 and the prosthesisthreaded portion 196 (shown in FIG. 3) of the insertion/extractioncavity 184. In other embodiments, however, the insertion/extractioncavity axis 200 need not extend through the center of the instrumentreceiving portion 188. When the insertion/extraction cavity axis 200 andthe proximal stem axis 128 are projected onto a coronal plane, theinsertion/extraction cavity axis 200 is not oriented in a direction thatis substantially parallel to the proximal stem axis 128 but insteadextends at the angle A relative to the proximal stem axis 128. Inparticular, the insertion/extraction cavity axis 200 extends at theangle A proximally and medially to the proximal stem axis 128. In atleast one embodiment, the angle A is in the range of approximately onethrough approximately forty-five degrees. The angle A in one embodimentis twelve degrees relative to the proximal stem axis 128.

In one embodiment, the insertion/extraction cavity 184 is oriented in adirection that is approximately parallel to the shoulder 176. As notedabove, the shoulder 176 is formed due to the neck lateral portion 164extending more medially at the neck proximal end portion 152 than at theneck distal end portion 156 (shown in FIG. 2). In other words, theshoulder 176 extends laterally as it extends distally relative to theproximal surface 180. Accordingly, when the stem 104 and the neckportion 108 (shown in FIG. 2) are viewed in the coronal plane, theshoulder 176 is not oriented in a direction that is substantiallyparallel to the proximal stem axis 128 but instead extends at an angle Arelative to the proximal stem axis 128.

In one embodiment, there is provided a kit including a plurality offemoral prostheses of different sizes and shapes allowing the physicianto select the best fitting prosthesis from the kit to insert into aparticular patient's femur. The best fitting prosthesis is determinedby, among other considerations, the morphology and topography of thepatient's femur. Accordingly, to provide a useful range of fits, eachfemoral prosthesis in the kit has a shoulder 176 oriented at an angle Arelative to the proximal stem axis 128 that is different than the angleof each of the other femoral prostheses in the kit. In this embodiment,the angle of the insertion/extraction cavity 184 relative to theproximal stem axis 128 of each of the femoral prostheses in the kit isapproximately equal to the angle of the shoulder 176 relative to theproximal stem axis 128 of the smallest femoral prosthesis in the kit. Inthis embodiment, the angle of the shoulder 176 relative to the proximalstem axis 128 of the smallest femoral prosthesis in the kit isapproximately twelve degrees. An advantage of this embodiment is thatthe physician has the same feel, and exerts the same forces in the samedirections, while inserting any of the femoral prostheses into thepatient's femur (as described below), because the insertion/extractioncavity 184 is oriented at the same angle regardless of the size or shapeof the particular prosthesis. In another embodiment, the angle of theinsertion/extraction cavity 184 relative to the proximal stem axis 128of each of the femoral prostheses in the kit is approximately equal tothe angle of the shoulder 176 of that femoral prosthesis relative to theproximal stem axis 128.

Returning to FIG. 2, the femoral head fitting 112 extends proximallyfrom the neck proximal end portion 152 and includes a coupling surface228 extending around the femoral head fitting 112 and tapering inwardlysuch that the femoral head fitting 112 is configured to mate for afriction fit with a complementary taper of a ball portion (not shown).Taken together, the femoral prosthesis 100 and the ball portion completea femoral implant that is used to replace the femoral head of a patientduring hip arthroplasty.

Turning now to FIG. 5, an instrument 300 is provided that is configuredto enable insertion of the femoral prosthesis 100, described above andshown in FIG. 2, into and removal of the femoral prosthesis 100 from apatient's femur during hip arthroplasty. The instrument 300 includes aninstrument body or housing 312 and a shaft 316. The housing 312 definesa housing axis 320 and includes a housing impact end portion 324, ahousing engagement end portion 328, a longitudinal opening 332, and aninstrument keyed portion 336. The housing axis 320 extends axiallythrough the center of the housing 312 through the housing impact endportion 324 and the housing engagement end portion 328 and, in thisembodiment, is coincident with an impact axis 308. The impact axis 308is the axis along which force is transferred to a femoral prosthesissuch as the femoral prosthesis 100. In another embodiment, however, thehousing axis 320 need not be coincident with the impact axis 308.

The housing impact end portion 324 is arranged opposite the housingengagement end portion 328. The longitudinal opening 332 extends throughthe housing 312 along the housing axis 320 from the housing impact endportion 324 to the housing engagement end portion 328. The instrumentkeyed portion 336 is located at the distal end of the housing engagementend portion 328.

The shaft 316 defines a shaft axis 340 and includes a shaft impact endportion 344, and a shaft engagement end portion 348, which includes aninstrument threaded portion 352. The shaft axis 340 extends axiallythrough the center of the shaft 316 through the shaft impact end portion344 and the shaft engagement end portion 348. The shaft 316 is sized andconfigured to be rotatably received and retained within the longitudinalopening 332 of the housing 312 such that the shaft axis 340 iscoincident with the housing axis 320. In this embodiment, the shaft axis340 is, consequently, also coincident with the impact axis 308. Inanother embodiment, however, the shaft axis 340 need not be coincidentwith the impact axis 308. When the shaft 316 is received within thehousing 312, the shaft impact end portion 344 is adjacent the housingimpact end portion 324, the shaft engagement end portion 348 is adjacentthe housing engagement end portion 328, and the shaft 316 is rotatablerelative to the housing 312.

The shaft impact end portion 344 includes a knob 354 having an impactsurface 356. The knob 354 of the shaft impact end portion 344 extendsoutwardly of housing impact end portion 324 such that the knob 354protrudes beyond the housing impact end portion 324. The knob 354 isoperably connected to the shaft impact end portion 344 and is configuredto be gripped. The shaft 316 can be rotated relative to the housing 312by rotating the knob 354 where it protrudes beyond the housing impactend portion 324. The impact surface 356 is arranged proximally on theknob 354 such that it aligns with and is substantially orthogonal to theshaft axis 340. Accordingly, an impact applied to the impact surface 356is transferred through the shaft 316 along the shaft axis 340.

The instrument threaded portion 352 protrudes from the housingengagement end portion 328 such that the threads 360 of the instrumentthreaded portion 352 are exposed. The instrument threaded portion 352 issubstantially aligned with the shaft axis 340. As mentioned above, theshaft 316 is configured such that, when the knob 354 on the shaft impactend portion 344 is rotated, the shaft engagement end portion 348 is alsorotated, thereby rotating the instrument threaded portion 352 relativeto the housing engagement end portion 328.

As shown in FIG. 6, the instrument 300 is arranged and configured suchthat the housing engagement end portion 328 and the shaft engagement endportion 348 engage the insertion/extraction cavity 184 of the femoralprosthesis 100 to facilitate insertion of the femoral prosthesis 100into a patient's femur and removal of the femoral prosthesis 100 from apatient's femur during hip arthroplasty. In particular, the prosthesiskeyed portion 192 is configured to couple with the instrument keyedportion 336, and the prosthesis threaded portion 196 is configured tocouple with the instrument threaded portion 352.

In operation, to use the instrument 300 to facilitate insertion of thefemoral prosthesis into a patient's femur, the instrument threadedportion 352 is first inserted into the instrument receiving portion 188to generally align the instrument 300 with the insertion/extractioncavity 184. Once the threaded portion has been received within theinstrument receiving portion 188, the instrument keyed portion 336 isinserted into the prosthesis keyed portion 192 to maintain the alignmentof the instrument 300 with the femoral prosthesis 100.

Next, the instrument threaded portion 352 is rotated relative to thehousing 312 by rotating the knob 354 on the shaft impact end portion 344(shown in FIG. 5). Because the instrument keyed portion 336 is matedwith the prosthesis keyed portion 192, the housing 312 is prevented fromrotating relative to the femoral prosthesis 100. Accordingly, when theinstrument threaded portion 352 is rotated relative to the housing 312,the instrument threaded portion 352 is also rotated relative to thefemoral prosthesis 100. Thus, the instrument threaded portion 352extends into and threadably engages the prosthesis threaded portion 196in the insertion/extraction cavity 184. In this embodiment, engagementof the instrument threaded portion 352 with the prosthesis threadedportion 196 couples the instrument 300 with the femoral prosthesis 100such that the instrument 300 is restricted in movement away from thefemoral prosthesis 100. In another embodiment, threaded portions neednot be used to couple the instrument 300 with the femoral prosthesis100, but the instrument 300 is coupled to the femoral prosthesis 100 inanother way which restricts movement of the instrument 300 away from thefemoral prosthesis 100. For example, either a collet or a bayonet claspis used to couple the instrument 300 with the femoral prosthesis 100 insuch a way as to restrict movement of the instrument 300 away from thefemoral prosthesis 100.

Once the instrument threaded portion 352 has fully engaged theprosthesis threaded portion 196, the impact axis 308 is substantiallycoincident with the insertion/extraction cavity axis 200. Accordingly,because the insertion/extraction cavity axis 200 is not oriented in adirection that is substantially parallel to the proximal stem axis 128but instead extends at an angle A relative to the proximal stem axis128, the impact axis 308 also is not parallel with the proximal stemaxis 128. An advantage of orienting the impact axis 308 at an angle Arelative to the proximal stem axis 128 is that the physician can avoidunnecessary interference with the patient's musculoskeletal system inthe hip joint. Because the impact axis 308 is oriented at an angle A,the physician need not have an orthogonal line of access relative to thefemoral prosthesis 100 to insert or remove the femoral prosthesis. Themost effective combination of leverage and access is achieved byorienting the impact axis 308 at an angle A that is in a range ofapproximately one degree through approximately forty-five degreesrelative to the proximal stem axis 128.

An impact is then applied to the instrument 300 and transferred throughthe instrument 300 to the attached femoral prosthesis 100. Morespecifically, when an impact force is applied to the impact surface 356(shown in FIG. 5), the impact force is transferred through the impactsurface 356, the knob 354, the shaft 316, and the threaded portion 352,successively, to the femoral prosthesis 100, thereby facilitatinginsertion of the femoral prosthesis 100 into the patient's femur.Because the impact axis 308 is coincident with the insertion/extractioncavity axis 200, the impact force is transferred fully and directly intothe femoral prosthesis 100 without generating a moment around theinstrument threaded portion 352 or applying shear stress to theinstrument threaded portion 352. Accordingly, using the instrument 300in combination with the femoral prosthesis 100 during hip arthroplastyfacilitates the insertion of the femoral prosthesis 100 into thepatient's femur with more efficiency and less risk for error.

In one embodiment, the housing 312 includes internal threads (not shown)such that when the instrument threaded portion 352 is rotated relativeto the housing 312, the shaft 316 travels axially within the housing312. Accordingly, increasing engagement of the instrument threadedportion 352 with the prosthesis threaded portion 196 causes the shaft316 to travel distally within the housing 312. Distal movement of theshaft 316 within the housing 312 is limited by contact of the knob 354on the shaft impact end portion 344 (shown in FIG. 5) with a housingproximal surface 364 on the housing impact end portion 324. In thisembodiment, an impact force applied to the impact surface 356 istransferred to the femoral prosthesis 100 through the housing 312 inaddition to the shaft 316.

Additionally, in this embodiment, to facilitate the transfer of theimpact force to the femoral prosthesis 100 through the housing 312, theinstrument keyed portion 336 is configured to contact the prosthesiskeyed portion 192. Specifically, an instrument keyed portion surface 338is configured to contact and rest flatly on a prosthesis keyed portionsurface 194. The prosthesis keyed portion surface 194 is arrangedsubstantially orthogonally relative to the insertion/extraction cavityaxis 200. When an impact force is applied to the impact surface 356(shown in FIG. 5), the impact force is transferred through the impactsurface 356, the knob 354, the housing proximal surface 364, theinstrument keyed portion 336, and, ultimately, the instrument keyedportion surface 338, successively. The arrangement of the prosthesiskeyed portion surface 194 relative to the insertion/extraction cavityaxis 200 (and thus relative to the impact axis 308) causes the impactforce to be transmitted through the instrument keyed portion 336 to thefemoral prosthesis 100 in a direction along the instrument keyed portion336 such that neither the instrument threaded portion 352 nor theinstrument keyed portion 336 experiences any shear stress. The transferof the impact force to the femoral prosthesis 100, thereby furtherfacilitates insertion of the femoral prosthesis 100 into the patient'sfemur with greater efficiency and less risk for error.

In embodiments wherein the instrument 300 is used only for insertion,through the processes described above, the threaded portions 196 and 352may be omitted. In an embodiment wherein the instrument 300 does notinclude threaded portions 196 and 352, the shaft engagement end portion348 is used solely for alignment and the only area of contact betweenthe instrument 300 and the femoral prosthesis 100 is where theinstrument keyed portion surface 338 contacts the prosthesis keyedportion surface 194. Put another way, the impact is transferred to thefemoral prosthesis 100 only through the housing 312 of the instrument300.

In embodiments wherein the threaded portions 196 and 352 are included,however, the instrument 300 may be used for extracting, in addition toinserting, the femoral prosthesis 100. Specifically, the threadedportions 196 and 352 of the prosthesis and the instrument, respectively,enable use of the prosthesis 100 and the instrument 300 for extractionfrom the femur in addition to insertion into the femur. The process bywhich the instrument 300 is used for insertion of the prosthesis 100 isdescribed above. The process by which the instrument 300 is used forextraction of the prosthesis 100 differs from the insertion process inthat the threaded portions 196 and 352 engage with one another, suchthat applying force to the instrument 300 in a direction away from theprosthesis 100 will pull the prosthesis 100 away from the femur, therebyextracting the prosthesis 100 from the intermedullary canal.

By way of example, the instrument 300, in some embodiments, includesfeatures that enable the impact force to be applied in the oppositedirection relative to the insertion impact. In particular, theinstrument 300 is configured such that the knob 354 aligns with and issubstantially orthogonal to the shaft axis 340 such that an impactapplied to the underside of the knob 354 is transferred through theshaft 316 along the shaft axis 340. Alternatively, the housing 312includes a flange (not shown) which extends outwardly from the housingaxis 320 at the shaft impact end portion 344 and is configured toreceive an impact applied in a direction away from the shaft engagementend portion 348. In this way, the instrument 300 is still used with thefemoral prosthesis 100 but, because the impact is applied in theopposite direction, the instrument 300 facilitates extraction of, ratherthan insertion of, the femoral prosthesis 100. Accordingly, using theinstrument 300 in combination with the femoral prosthesis 100 during hiparthroplasty facilitates the extraction of the femoral prosthesis 100from the patient's femur with more efficiency and less risk for error.

Consequently, while the instrument 300 in FIG. 5 is configured to bothinsert and extract a femoral prosthesis 100, in some embodiments, aseparate instrument is used to insert a femoral prosthesis 100 than toextract a femoral prosthesis 100.

The foregoing detailed description of one or more embodiments of thefemoral prosthesis and instrument has been presented herein by way ofexample. It will be recognized that there are advantages to certainindividual features and functions described herein that may be obtainedwithout incorporating other features and functions described herein.Moreover, it will be recognized that various alternatives,modifications, variations or improvements of the above-disclosedembodiments and other features and functions, or alternatives thereof,may be desirably combined into many other different embodiments, systemsor applications. Presently unforeseen or unanticipated alternatives,modifications, variations or improvements therein may be subsequentlymade by those skilled in the art which are also intended to beencompassed by the appended claims. Therefore, the spirit and scope ofany appended claims should not be limited to the description of theembodiments contained herein.

What is claimed is:
 1. A femoral prosthesis comprising: a stem includinga proximal end portion defining a proximal stem axis; a neck portionlocated proximally of the proximal end portion; and aninsertion/extraction cavity extending distally from a proximal surfaceof the neck portion and configured to couple with aninsertion/extraction instrument, the cavity defining aninsertion/extraction cavity axis which, when projected onto a coronalplane including the proximal stem axis, is not parallel with theproximal stem axis.
 2. The femoral prosthesis of claim 1, wherein whenthe insertion/extraction cavity axis is projected onto the coronal planethe insertion/extraction cavity axis extends proximally and mediallyfrom the proximal stem axis.
 3. The femoral prosthesis of claim 2,wherein the when the insertion/extraction cavity axis is projected ontothe coronal plane, the insertion/extraction cavity axis extendsproximally and medially from the proximal stem axis at an angle in therange of approximately one degree through approximately forty-fivedegrees.
 4. The femoral prosthesis of claim 2, wherein when theinsertion/extraction cavity axis is projected onto the coronal plane theinsertion/extraction cavity axis extends proximally and medially fromthe proximal stem axis at an angle of about twelve degrees.
 5. Thefemoral prosthesis of claim 4, wherein the stem is substantiallystraight.
 6. The femoral prosthesis of claim 2, wherein theinsertion/extraction cavity comprises: a keyed portion configured tomate with a keyed portion of the insertion/extraction instrument.
 7. Thefemoral prosthesis of claim 6, the keyed portion including a keyedportion surface arranged substantially orthogonally relative to theinsertion/extraction cavity axis.
 8. The femoral prosthesis of claim 6,the insertion/extraction cavity further comprising: a threaded portionconfigured to receive a threaded portion of the insertion/extractioninstrument.
 9. A femoral prosthesis system comprising: a femoralprosthesis including a femoral stem with a proximal end portion defininga proximal stem axis, a neck portion located proximally of the proximalend portion, and an insertion/extraction cavity extending distally froma proximal surface of the neck portion, the cavity defining aninsertion/extraction cavity axis which, when projected onto a coronalplane including the proximal stem axis, is not parallel with theproximal stem axis; and an insertion/extraction instrument including adistal end portion configured to couple with the insertion/extractioncavity.
 10. The system of claim 9, wherein when the insertion/extractioncavity axis is projected onto the coronal plane the insertion/extractioncavity axis extends proximally and medially from the proximal stem axis.11. The system of claim 10, wherein when the insertion/extraction cavityaxis is projected onto the coronal plane the insertion/extraction cavityaxis extends proximally and medially from the proximal stem axis at anangle in the range of approximately one degree through approximatelyforty-five degrees.
 12. The system of claim 10, wherein when theinsertion/extraction cavity axis is projected onto the coronal plane theinsertion/extraction cavity axis extends proximally and medially fromthe proximal stem axis at an angle of about twelve degrees.
 13. Thesystem of claim 10, wherein the femoral stem is substantially straight.14. The system of claim 10, the insertion/extraction instrument furtherincluding: a shaft defining an impact axis and configured such that theimpact axis is parallel with the insertion/extraction cavity axis whenthe insertion/extraction instrument is coupled with the femoralprosthesis.
 15. The system of claim 14, wherein the impact axis isaligned with the insertion/extraction cavity axis when theinsertion/extraction instrument is coupled with the femoral prosthesis.16. The system of claim 14, wherein: the insertion/extraction cavityincludes a first keyed portion; the insertion/extraction instrumentincludes a second keyed portion; and the first and second keyed portionsare configured to mate with each other in a keyed relationship.
 17. Thesystem of claim 16, wherein the first keyed portion includes a firstkeyed portion surface arranged substantially orthogonally relative tothe insertion/extraction cavity axis.
 18. The system of claim 16,wherein the insertion/extraction cavity further includes a threadedportion configured to receive a threaded portion of theinsertion/extraction instrument.
 19. The system of claim 18, wherein thethreaded portion of the insertion/extraction instrument is rotatablewith respect to the second keyed portion.
 20. A method of inserting afemoral prosthesis comprising: coupling an insertion/extractioninstrument with a proximal portion of a femoral component such that animpact axis defined by a shaft of the insertion/extraction instrument isnot parallel with a longitudinal axis defined by a stem portion of thefemoral prosthesis; inserting a distal end portion of the femoralprosthesis into a femur; and impacting a proximal end portion of theinsertion/extraction instrument.